Elsevier

Journal of Cleaner Production

Continuous BIM-based assessment of embodied environmental impacts throughout the design process

Abstract

Life Cycle Assessment (LCA) is a suitable method to analyse and improve the environmental impact of buildings. However, it is complex to apply in the design phase. Building Information Modelling (BIM) can help to perform LCA during the design process. Current BIM-LCA approaches follow two trends. Either they use complex models in detailed design phases, when it is late for major changes, or they are based on simplified approaches only applicable in early design stages. This paper proposes a novel method for applying LCA continuously over the entire building design process to assess the embodied environmental impacts by using the data provided by BIM with as much accuracy as possible in each stage. The method uses different LCA databases with different levels of detail for the specific level of development (LOD) of the BIM. Since different building elements are not modelled with identical LODs in each design phase, the assessment of embodied environmental impacts is conducted by consistently mixing the LCA databases, which is possible as long as the databases use identical background data. The method is applied to five design stages of a building case study. The results show that it is now possible to calculate the embodied impacts in all design stages while being consistent with the results from the completed project. The environmental impact in a certain design phase is always within the range of variability of the previous phase. Therefore, the method allows to estimate the final embodied environmental impact with increasing accuracy and by that provide information for decision-making throughout the whole design process.

Introduction

The architecture, engineering and construction (AEC) sector is one of the major carbon emitters and energy consumers. Since 1970, energy-related greenhouse gas (GHG) emissions from the operation of buildings have more than doubled, accounting for 19% of the total emissions in 2010 (IPCC, 2014). Next to the operational environmental impact, the embodied GHG emissions related to the production, replacement and end-of-life of building components are responsible for a larger share of global GHG emissions. The manufacturing of building materials alone represents 5–10% of the global GHG emissions (Habert et al., 2012). This highlights the importance of considering the entire life cycle of buildings.

The interest of Life Cycle Assessment (LCA) for the construction sector has been noted in several review papers (Ortiz et al., 2009; Singh et al., 2011; Buyle et al., 2013; Cabeza et al., 2014; Islam et al., 2015; Abd Rashid and Yusoff, 2015; Soust-Verdaguer et al., 2016; Anand and Amor, 2017; Geng et al., 2017). LCA is widely recognized as a powerful tool to predict the environmental impacts of buildings during their life cycle (Chen et al., 2010; Russell-Smith et al., 2015). LCA covers the entire life cycle of buildings from raw materials extraction and processing, manufacturing of building components, to use and end-of-life. The method as described in ISO 14040 (ISO 14040, 2006) consists of four phases: goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation (ISO 14040, 2006; ISO 14044, 2006). Usually, LCA studies of products are structured according to these four phases. For LCA of buildings, predefined datasets for the materials or components used in the building are used in most cases. As such, the LCI and LCIA are merged into one step and simplified ( Lasvaux and Gantner, 2013). Basically, only a bill of quantities (BoQ) is needed that is multiplied with values of the respective datasets from the LCA database. Then, the results can be summed up under consideration of the reference service life of the individual components. Nevertheless, the LCA of buildings is a complex task because of the large amount of information required and time-consuming nature of the method (Zabalza Bribián et al., 2009). Most time and effort is needed to establish the BoQ and find the correct datasets in the building material LCA database. As a result, the LCA of buildings is commonly conducted at the end of the design process, when the necessary information is available, but it is too late to affect the decision-making process (Díaz and Antón, 2014). This dilemma for LCA of buildings is closely related to the nature of the design process. On the one hand, early design choices are responsible for a significant amount of the total environmental impacts (Attia et al., 2012; Shi and Yang, 2013; Häkkinen et al., 2015), but LCA cannot be fully applied because of the incompleteness of the data. On the other hand, LCA can no longer successfully be used as a decision-making tool in late design stages because making changes is too costly (Hollberg and Ruth, 2016).

Building Information Modelling (BIM) can facilitate establishing a BoQ and support project teams by providing immediate insight into how design decisions affect the building performance (Hill Construction, 2010). Hence, BIM is increasingly used to explore design solutions to improve the life cycle performance (Eleftheriadis et al., 2017; Wong and Zhou, 2015). BIM-LCA integration is a powerful approach to perform LCA for buildings during the design process and the growing number of applications on BIM-based LCA is underlined in recent papers (Eleftheriadis et al., 2017; Chong et al., 2017; Soust-Verdaguer et al., 2017). However, the existing studies present methods for conducting BIM-based LCA in a specific design phase. They usually either focus on an early concept phase or a very detailed design stage when all material information is known. The methods cannot be used as a design process-integrated decision tool, because they do not consider the entire building design process and the evolution of available information throughout the process. Moreover, most papers on BIM-based LCA methods do not declare the Level of Development (LOD) for the LCA (Soust-Verdaguer et al., 2017). The LOD defines the minimum content requirements for each element of the BIM at five progressively detailed level of completeness, from LOD 100 to LOD 500; see (AIA, 2013a; AIA, 2013b). Thus, the LOD of each element represents the information content of the object, based on which LCA can be performed. The LOD of the elements undergo an evolution from low to high according to the needs of each design phases. However, not all elements undergo this evolution at the same time, as they are not defined simultaneously. Typically, structural elements are defined early in the design process, while materials for interior surfaces might even be changed after the construction of the building has started.

The goal of this paper is to provide a framework allowing to use LCA as a consistent decision-making support tool regarding the embodied environmental impacts of a building during all phases of the design process. The novel approach considers the available information in the BIM model as accurate as possible in every design phase. This is achieved by mixing LCA databases for building elements and materials with different levels of detail and matching them according to the individual LOD of the various BIM components. This approach has not been considered by any method described in the reviewed literature and allows to overcome the current problem of disconnection between building LCA tools for early and late design phases.

The paper is structured as follows. Section 2 presents a literature review, which is organized around the two different trends to conduct BIM-based LCA – either using simplified models in early design phases or very detailed approaches in late design phases. In section 3, the development of the framework for assessing embodied environmental impact continuously is described for the Swiss context. The building is structured into eleven elements according to the Swiss cost calculation standard. The design process is divided into five main phases according to the Swiss practice. Here, the tendering and construction phase are also regarded as design phases, because decisions on materials are still taken in these phases and influence the environmental performance of the building. Furthermore, the LOD evolution of the building elements is assumed based on the typical Swiss architecture practice. The framework is tested by means of a case study of a multi-family house described in section 4. The results of applying the framework are described in section 5, before the main contributions and limitations are discussed in section 6. The paper concludes in section 7.

Section snippets

Literature review

Several studies have been conducted to enhance the dialogue between BIM and LCA for sustainable construction (Wong and Zhou, 2015; Kylili et al., 2015). BIM is oriented to the modelling and communication of both graphic and non-graphic information to enable the extraction of quantities, cost estimations and material properties for buildings, facilities and infrastructures (Cheung et al., 2012). BIM allows different stakeholders to manage digital data of the building throughout its entire life

Method

The development of the framework is described for the Swiss context. The same approach can be followed to define frameworks for other countries as well. The approach is based on the application of different levels of detail of the embodied impact calculation depending on the available information, respectively LOD of the BIM. As such, the method consist of three main steps (Fig. 1):

1.

Definition of an evolution of LOD

2.

Consistent combination of LCA databases

3.

Link between LODs and LCA databases

Application to a case study

The method is applied using a case study of a multi-family house. The building in the case study is based on a real building called WoodCube (Fig. 5). The five-story building measures approximately 15 m × 15 m and provides eight apartments. Some small modifications to the geometry were made to simplify it for the case study (Hollberg and Ruth, 2016).

All material properties are obtained from a published LCA report (Hartwig, 2012). Length, area and volume of different materials and components are

Results

The results for the GWP of each building element for different planning phases are shown in Fig. 6. The results for the PP phase are provided for the entire building elements because they are modelled at LOD 100. The results for the later design stages are provided for the individual components and represent a mix of databases. The results for the average, minimum and maximum of the building elements and components at LOD 100, LOD 200, and LOD 300 are provided in Table SI1 of the Supplementary

Discussion

The application of the proposed method in a case study shows that it is possible to continuously assess the embodied impacts throughout the building design process. Fig. 6 shows that the variability decreases from the early design phases to the final ones for most building elements because more refined data are used at higher LODs. As a result, the GWP in a certain design stage is within the variability of the previous one. The main contribution of the research is to predict the GWP during the

Conclusion

LCA is commonly difficult to apply during the entire building design process because the necessary data are only complete in the latest phases. However, the present study shows that it is possible to continuously assess the embodied environmental impacts in all phases of the building design process using BIM and mixing LCA databases with different level of detail. The suggested approach consists of structuring the building into functional elements and construction categories because they are

Acknowledgement

The authors would like to thank Gianluca Genova for his great support, ideas and participation in this study.

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